Mobile stations offer sophisticated capabilities for determining their position using a variety of resources, including those resources provided by wireless communication networks. New software applications residing on mobile stations, such as those related to personal productivity, social networking, advertising, e-commerce, and/or other forms of data acquisition, may utilize position information to provide new features and services to consumers. Moreover, some regulatory requirements of various jurisdictions may require a network operator to report the location of a mobile station for emergency services.
In conventional digital cellular networks, position location capability can be provided by various time and/or phase measurement techniques. For example, in CDMA networks, one position determination approach used is Advanced Forward Link Trilateration (AFLT). Using AFLT, a mobile station may compute its position from phase measurements of pilot signals transmitted from a plurality of base stations. Improvements to AFLT have been realized by utilizing hybrid position location techniques, where the mobile station may employ a Satellite Positioning System (SPS) receiver. The SPS receiver may provide position information independent of the information derived from the signals transmitted by the base stations. Moreover, position accuracy can be improved by combining measurements derived from both SPS and AFLT systems using conventional techniques.
However, conventional position location techniques based upon signals provided by SPS and/or cellular base stations may encounter difficulties when the mobile station is operating within a building and/or within urban environments. In such situations, signal reflection and refraction, multipath, and/or signal attenuation can significantly reduce position accuracy, and can slow the “time-to-fix” to unacceptably long time periods. These shortcomings may be overcome by having the mobile station exploit signals from other types of wireless networks, such as Wi-Fi (e.g., IEEE 802.11x standards) or WiMAX (e.g., IEEE 802.16 standards), to derive position information. Conventional position determination techniques used in these other types of wireless networks may utilize range-based position determination techniques. The range-based position determination techniques may estimate distance information using Round Trip Time (RTT) measurements and/or signal strength measurements (e.g., Received Signal Strength Indicator (RSSI)) derived from signals utilized within such networks. The range based position determination may be used for any network device within these networks, such mobile stations and/or access points (APs) which are placed at unknown positions. However, indoor environments can present challenges for reliable range measurements due to the complexity of the radio frequency (RF) environment and multipath.
Moreover, the network devices themselves may introduce various biases that can affect range determination. For example, RTT measurement techniques may be affected by time biases introduced by time delays incurred as wireless signals propagate through various devices in the network. Utilizing RSSI measurements for accurate ranging may be affected by amplitude biases introduced by transmission power differences and/or various gains used in RF and signal processing paths of network devices. In practice, when employing conventional range-based positioning techniques, estimating and removing time and amplitude biases may involve time-consuming pre-deployment fingerprinting and/or calibration of the network devices.
Accordingly, it may be desirable to implement efficient compensation techniques which can address time and amplitude biases to improve range-based position determination, while avoiding costly pre-deployment efforts and/or changes to the network infrastructure.